Phased antenna arrays are commonly used to scan an antenna beam electronically. The array normally consists of several antenna elements, such as dipoles or slots, waveguides or horns, and microstrip antennas or other printed configurations. In such arrays, the direction of the array beam can be steered electronically by introducing proper phase shifts to the input excitation of individual elements. Such phase shifting can be achieved using one active phase shift network for each element.
The configurations of the array depend on the application to which the antenna is put and, in principle, can be designed to provide any beam scanning capability, but, as a practical matter, difficulties arise. One of the significant problems with existing phased arrays is the cost of the antenna and its beamforming network.
The beamforming network consists of power dividers which provide the required power level to each antenna element and phase shifters which generate the phase shifts for beam scanning. In medium-to-high power applications, in particular, for dual or multifrequency applications, digital phase shifters are used to eliminate the intermodular distortion.
When the array must be scanned in small angular steps and over a large region of space, multiple bit phase shifters are needed, which increases the antenna cost and insertion loss. The overall beamforming network then becomes too complex and expensive to implement.
A second problem with existing phase arrays results from the insertion loss of the beamforming network, which increases with the array size and higher bit states of the phase shifters. These losses decrease the gain of the array and limit the peak achievable gain for large or highly-scanned arrays. Additional difficulties arise from the complexity of the beam scanner to control the phase states.
The present invention seeks to overcome these prior art problems and to provide a phased scanning antenna which operates satisfactorily yet does so at decreased cost and complexity and decreased insertion losses.
A search of the prior art has been conducted in the United States Patent and Trademark Office for patents relevant to the principles of the present invention. As a result of that search, the following U.S. Pat. Nos. have been noted as the most relevant: 3,541,557, 4,070,676, 4,415,900, 3,713,162, 4,089,003, 4,521,781, 3,739,386, 4,218,682, 4,605,932, 3,803,623, 4,320,402, 3,811,128, 4,379,296, It is believed that none of this prior art discloses the principles of the invention described herein.